Synthesis of aliphatic nitriles by pyrolysis and thermal cleavage of hydrazones, ketazines, ketimines and ketoximes



United States Patent SYNTHESIS OF ALIPHATIC NITRILES BY PYROLY- SIS AND THERMAL CLEAVAGE OF HYDRA- ZONSES, KETAZINES, KETIMINES AND KETOX- IME John L. Anderson, Wilmington, Del., assignor to E. I. du Pont dc Nemours and Company, Wilmington, Del., a corporation of Delaware Application November 5, 1953, Serial No. 390,420

12 Claims. (Cl. 260465.1)

No Drawing.

This invention relates to the preparation of nitriles.

More particularly this invention relates to a new process chemical or catalytic dehydration of amides, dehydration of cyanohydrins, and reaction of alkyl halides with alkali metal cyanides. However, because of the commercial importance of aliphatic nitriles, there is continued interest in finding new methods for their synthesis which ofier ease of operation over known methods or advantages of cost reduction from available starting materials.

It is an object of this invention to provide a new process for the preparation of aliphatic nitriles. A further object is to provide an easily operated process for preparing aliphatic nitriles from available starting materials. Other objects will appear hereinafter,

These objects are accomplished according to this invention by the following process for obtaining aliphatic nitriles which comprises pyrolyzing aliphatic hydrazones,

ketazines, ketimines and ketoximes at a temperature in excess of 375 C., and condensing the pyrolysate containing aliphatic nitrile and other pyrolysis products.

In one convenient method of operation, the aliphatic hydrazone, ketazine, ketimine, or ketoxime is passed through a reaction ZOE-8 heated to above 375 C. and the pyrolysis products are rapidly cooled to a temperature below 0 C. In practice, the reaction products are led directly from the reaction zone into a cold receiver. The exact temperature at which the receiver is maintained depends upon the nature of the reaction products. In some instances, temperatures as low as liquid nitrogen are useful, in others solid carbon dioxide/ acetone temperatures are adequate, while in others -50 C. will sufiice. The composition of the pyrolysis products can be determined either by mass spectrometry as in Example III or by infrared, as inthe remaining examples. The nitriles produced in accordance with this invention can be separated from other pyrolysis products, and purified, by distillation at normal pressure or at pressures below atmospheric, or by other means well known to those skilled in the art.

The pyrolysis can be effected in reaction vessels which are constructed of materials which are inert to the nitriles and to their precursors. Satisfactory materials are heatresistant glass, quartz, and inert metals. The vessel in which the pyrolysis is eflected is conveniently a cylindrical tube packed with an inert material, such as granular quartz, to improve heat transfer. Heat is applied to the reaction vessel by external means and a convenient source is an electrical heating coil.

The pressure at which the pyrolysis is effected is not critical but it is preferred to use pressures of 10 to 20 mm. or less. Especially good results are obtained when the pressure in the system (measured at a point following the cold receiver) is maintained at less than tenmicrons.

Patented Nov. 13, 1956 "ice The temperature at which. the pyrolysis is effected is in excess of 375 C. Usually, however, the pyrolysis is elfected at temperatures in the range of 400 to 1000 C. Because the best results from the standpoint of yield of desired products and reaction times are achieved in the range of 600 to 870 C., the pyrolysis is usually carried out at a temperature in this range.

The time of reaction depends on the pressure and temperature employed. It the pyrolysis is effected at temperatures of the order of 600 to 1000 C. and pressures of less than 10 microns, the time of reaction is usually one second or less. On the other hand, using higher pressure, e. g., 10 to 20 mm. and temperatures of the order of 375 to 600 C. the required reaction time may be longer.

The examples which follow are submitted to illustrate and not to limit this invention. Parts are by weight, unless otherwise stated.

EXAMPLE I Ten parts of acetoneazine are distilled through a cylindrical quartz tube (1 x 12") filled with quartz chips and heated at 700 C., the pressure in the system being held at approximately one micron of mercury (measured between the vacuum pump and the cold receiver). The pyrolysis products from the hot tube are led through a liquid nitrogen trap in which they condense. Analysis of these products by infrared absorption spectra shows ethane and acetonitrile to be present as major constituents. Similar results occur when the pyrolysis is carried out at 800 C.

EXAMPLE II Twenty parts of cyclohexanoneazine are dropped slowly through the apparatus and under the conditions described in Example I and the products condensed at liquid nitrogen temperatures. The major volatile pyrolysis products are acrylonitrile, C4 nitriles, and ethylene, as shown by infrared analysis.

EXAMPLE III Acetonitrile 2 Propionitrile 8 Acrylonitrile 58 C4 saturated uitrile 4 C4 unsaturated nitrile 20 C5 unsaturated nitrile 4 Cyanoprene (2-cyanobutadiene-l,3) 4

EXAMPLE IV Pyrolysis at 850 C. by sublimation of 10 parts of cyclopentanoneoxime through the system and under the pressure conditions described in Example I gives substantial quantities of ethylene and acrylonitrile together with hydroxyl group containing compounds, as determined by infrared analysis.

EXAMPLE V Ten parts of acetoneazine are passed through the apparatus and under the pressure conditions described in Example I at 200, 300, 400, 500, and 600 C. Infrared analysis shows that at 200 and 300 C., acetoneaziue is recovered unchanged, while at 400 C. and above, acetonitrile and ethane in increasing amounts are obtained.

EXAMPLE VI Ten parts of acetoneoxime are pyrolyzed at 800 C. in the apparatus and under the pressure conditions described in Example I. Infrared analysis shows that acetonitrile and ethane are the major pyrolysis products. No acetoneoxime is found in the pyrolysis products.

EXAMPLE VII wherein R and R are acyclic aliphatic groups, or when joined together with the carbon atom to which they are attached form a cycloaliphatic group, and particularly are alkyl radicals, preferably of 1 to 12 carbon atoms, or alkylene radicals which together with the carbon atom to which they are attached form a carbocyclic ring, preferably of 5 to 7 ring carbon atoms, and X is hydrogen, or hydroxyl, or alkoxy, particularly of l to 12 carbon atoms, or acyloxy, preferably of 1 to 12 carbon atoms, or monovalcnt aliphatic hydrocarbon, especially alkyl, particularly of 1 to 12 carbon atoms, or amino, or

wherein R and R have the previously indicated meanings.

In the left hand side of the table below are listed specific compounds coming within the scope of the process of this invention which when substituted for acetoneazine in the process of Example I give the products indicated in the right column.

Table Reactant Major Nitrilc Reaction Products Pentanone-3 hydrazone Reactant Major Nitrile Reaction Products Methyl isopropylketoxime O H C=NOH Acrylonitrile, CH =GHCN.

Acetonitrile, CHSCN.

0113-0 H OH3 Isobutyronitrile,

OHa-CH(OH )ON. E thylcyclopentanoneoxime lfiTO H C H Acrylonitrile, CHz=C HC N. 2-Ethylacrylonitrile, H 0 0 CHa=C (C2H )O N.

\ 2-E thylcrotonitriley C211 CHzCH=C(CzH )CN. H; o o H,

Acetoneoxiine acetate CH =NO 0-0113 Acetonitrilo, CHsCN.

Methyl ether of acetoneoxirne C=NO CH3 *Acetonitrile, CHBCN. CH3

N-Dodecylirnine of cyclohexanone OH; 1 Hi0 C=N-C13H25 Acrylonitrile, CHZ=CHLN.

I Acetonitrile, OHECN. H2O CH2 C3, C4 and C5 Nitriles.

In addition to the above, there may be used the N-ethylimine of acetone, isophoroneoxime, methyl-nnonyl ketoxime, and the like, with similar results.

The synthesis of aliphatic nitriles by the thermal cleavage of aliphatic hydrazones, ketazines, ketimines and ketoximes according to the process of this invention makes accessible new sources of nitriles. The nitriles thus prepared are of interest in themselves and as intermediates for other products of technical and commercial interest.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. Process for obtaining aliphatic nitriles which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the range of 400 to 1000 C. a compound of the general formula C=NX RI wherein R and R' are selected from the class consisting of acyclic aliphatic nadicals and aliphatic radicals which together with the carbon atom to which they are attached form a cycloaliphatic radical and X is selected from the class consisting of hydrogen, hydroxyl, alkoxy, acyloxy, monovalent aliphatic hydrocarbon radicals, amino and the group wherein R and R are defined as aforesaid, and condensing the pyrolysis products containing aliphatic nitrile of a lesser number of carbon atoms than the unpyrolyzed compound.

2. Process for obtaining aliphatic nitrilcs which comprises passing through a pyrolysis zone and thermally cleaving in the absence of a catalyst at 600 to 1000 C. a compound of the general formula wherein R and R are selected from the class consisting of acyclic aliphatic radicals and aliphatic radicals which together with the carbon atom to which they are attached form a cycloaliphatic radical and X is selected from the class consisting of hydrogen, hydroxyl, alkoxy, acyloXy, monovalent aliphatic hydrocarbon radicals, amino and the group wherein R and R are defined as aforesaid, passing the pyrolysis products containing aliphatic nitrile of a lesser number of carbon atoms than the unpyrolyzed compound directly into a cold receiver and rapidly cooling said pyrolyzed products therein.

3. Process for obtaining aliphatic nitriles which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the range of 400 to 1000 C. a ketimine of the general formula O=NX wherein R and R are alkyl radicals of 1 to 12 carbon atoms and X is an alkyl radical of 1 to 12 carbon atoms, and condensing the pyrolysis products containing aliphatic nitrile of a lesser number of carbon atoms than said ketimine.

4. Process for obtaining acetonitrile which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the range of 400 to 1000 C. the N-methylimine of acetone, and condensing the pyrolysis products containing acetonitrile.

5. Process for obtaining aliphatic nitriles which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the range of 400 to 1000 C. a hydrazone of the general formula C=N-X wherein R and R are alkyl radicals of l to 12 carbon atoms and X is amino, and condensing the pyrolysis products containing aliphatic nitrile of a lesser number of carbon atoms than said hydrazone.

6. Process for obtaining aliphatic nitriles which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature Within the range of 400 to 1000 C. a hydrazone of the general formula wherein R and R are alkylene radicals which together with the carbon atom to which they are attached form a carbocyclic ring of 5 to 7 carbon atoms and X is amino,

nitrile of a lesser number of carbon atoms than said hydrazone.

7. Process for obtaining acrylonitrile which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the range of 400 to 1000 C. pentanone-B-hydrazone, and condensing the pyrolysis products containing acrylonitrile.

8. Process for obtaining acrylonitrile which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the range of 400 to 1000 C. cyclohexanoneazine, and condensing the pyrolysis products containing acrylonitrile.

9. Process for obtaining aliphatic nitriles which cornprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the range of 400 to 1000 C. a ketoxime of the general formula C=N-X RI wherein R and R are alkyl radicals of 1 to 12 carbon atoms and X is hydroxyl, and condensing the pyrolysis products containing aliphatic nitrile of a lesser number of carbon atoms than said ketoxime.

10. Process for obtaining aliphatic nitriles which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature Within the range of 400 to 1000" C. a ketoxime of the general formula C=NX wherein R and R are alkylene radicals which together with the carbon atom to which they are attached form a carbocyclic ring of 5 to 7 carbon atoms and X is hydroxyl, and condensing the pyrolysis products containing aliphatic nitrile of a lesser number of carbon atoms than said ketoxime.

11. Process for obtaining acrylonitrile which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature within the rang of 400 to 1000 C. cyclohexanoneoxime, and condensing the pyrolysis products containing acrylonitrile.

12. Process for obtaining acetonitrile which comprises pyrolyzing and thermally cleaving in the absence of a catalyst at a temperature Within the range of 400 to 1000 C. acetoneoxirne, and condensing the pyrolysis products containing acetonitrile.

OTHER REFERENCES Mailhe et al.: Bull. Soc. Chim., 23, 18-20 (1918). 

1. PROCESS FOR OBTAINING ALIPHATIC NUTRILES WHICH COMPRISES PHROLYZING AND THERMALLY CLEAVING IN THE ABSENCE OF A CATHALYST AT A TEMPERATURE WITHIN THE RANGE OF 400 TO 1000* C. A COMPOUND OF THE GENERAL FORMULA 